A typical conventional lamp socket of the foregoing type is shown in FIG. 4. The lamp socket 90 is substantially constructed of a cylindrical outer sleeve 91 made of a metallic sheet material, a central electrode assembly 92 including member 93 molded of an insulation material, such as a resin, into a circular disc-shaped contour, a button-shaped conductive terminal 94 having an electric wire connected thereto (see FIG. 5), and a coil spring 95 adapted to expand and contract within the outer sleeve 91 by a predetermined distance while supporting the central electrode assembly 92. A connector terminal 96 is typically fixedly secured to the other end (right-hand end as seen in the drawing) of the electric wire 94b for making connection to a wiring system in the vehicle (not shown).
With the conventional lamp socket 90 constructed in the above-described manner, assembly of the central electrode assembly 92 is achieved by caulking the left-hand end of electric wire 94b to a terminal portion 94a to prepare the button-shaped terminal 94. Thereafter, the button-shaped terminal 94 is manually inserted through a fitting hole 93a by inserting the right-hand end of electric wire 94b into the front side of member 93, and subsequently, connecting the right-hand end of electric wire 94b to the connector terminal 96 as shown in FIG. 5. In other words, each assembling operation is continuously performed by conducting a plurality of steps in following the order: caulking step (94a to 94b) .fwdarw.inserting step (94b through 93a) .fwdarw.caulking step (94b to 96), resulting in a complicated assembly operation. Consequently, there arises a problem that productivity of a production line for producing lamp sockets is degraded.